Skin structure Flashcards
intergumentary system
skin and its accessory structures
hair,nails, glands and sensory receptors
2 main parts of skin
epidermis and dermis
dermis thickness
1mm
epidermis thickness
0.1 mm
composition of dermis vs epidermis
epidermis mostly cells, dermis mostly components eg glands
thick skin
hairless
eg palms
fingertips, toes, soles
0.6-4.5 mm
thin skin
hairy all other parts of the body four layers density of hair follicles depends on where in the body hair follicles extend through the layers 0.1-0.15 mm
5 layers of what makes up epidermis
keratinocytes
stratum basale
single layer of columnar keratinocytes resting on basement membrane: site of production of new keratinocytes- stem cells
stratum spinosum
multiple rows of close packed, many sided keratinocytes linked by desmosomes
lots of keratin
stratum granulosum
rows of flattened keratinocytes containing darkly staining keratohyalin granules and lipid rich lamellar bodies- on release these form a hydrophobic, impermeable barrier
stratum lucidium
rows of clear, flat, keratin rich keratinocytes
present only in thick skin
stratum corneum
rows of dead, flat enucleate keratinocytes that have mostly cross-linked keratin fibres
have lipid in between
controlled apoptosis
as cells differentiate and reproduce, they are forced towards the skin’s surface, and are further from the blood supply and food supply, so die
how do keratinocytes differ in each layer
types of keratin change
evolve in shape
cell contents breakdown, rearrange and denucleate
keratins
cytoskeletal filament forming proteins
form branching, rope like bundles in cytoplasm
associate with desmosomes and hemidesmosomes at cell periphery
maintain structural integrity of epidermis, allow it to resist and dissipate mech forces
desmosomes
anchor epithelial cells to each other
lipid matrix
acts as skin’s main water proofing agent
hemidesmosomes
tie epidermal cells to fibres of the basal lamina
basal lamina/basement membrane
acellular layer between epidermis and dermis
where are melanocytes found
bottom of the epidermis
process of transfer of melanosomes
produced by golgi of melanocyte
melanosomes move into melanocyte cell processes, and epithelial cells phagocytize the tips of the melanocyte cell processes
The melanosomes have been transferred to the epithelial cells (keratinocytes in epidermis)
what happens next
melanosomes migrate to the peri-nucelar region and form a protective ‘cap’
what is skin colour determined by
amount of eumelanin and pheomelanin synthesised
not number of melanocytes
size of melanosomes
two regions of the dermis
papillary and reticular
papillary above, reticular below
how are desmosomes broken down
enzymes in stratum corneum
Langerhans cell
move within epidermis, APC
Present foreign antigens to T cells
macrophages of the skin
in the stratum spinosum layer
Merkel cell
sensory receptor cells
Make synapse-like contacts with somatosensory nerve endings
v sensitive touch receptors
in the stratum basale?
function of basal lamina
bridging structure, regulator of proliferation in stratum basale and movement of cells and molecules between epidermis and dermis
papillary matrix
loose connective tissue composed of fine elastic fibres with interspersed capillary loops and nerve fibres
lots of capillaries
Has Meissners corpuscles (touch receptors)
reticular matrix
dense connective tissue
randomly orientated collagen fibre, elastin, proteoglycans and glycosaminoglycans
has fibroblasts, macrophages and fat cells
cell types in the dermis
matrix synthesising fibroblasts, immune cells, vascular smooth muscle cells, and sweat gland myoepithelial cells
hair
grow from hair follicles in the dermis
composed of columns of dead, keratinised epithelial cells
originate from stratum basale in the hair bulb
function of smooth muscle
enables hair to stand on end, contraction elevates hair, forming goosebumps
function of sebaceous gland
produces sebum-oily lipids
lubricates hair shaft
function of blood vessels at the base of the hair follicle
give hair nourishment it needs to grow
types of glands general
endocrine and exocrine
how can exocrine glands be further categorised
based on structure and mode of secretion
3 modes of secretion
merocrine, apocrine (pinched off portion of the cell in secretion) and holocrine (dying cell releases secretory products)
2 main types of glands in the skin
sebaceous and sudoriferous
types of sudoriferous glands
apocrine and eccrine
apocrine
limited distribution merocrine secretion more viscous due to presence of lipids and proteins activity linked to emotional state active from puberty
eccrine
wide distribution duct opens at epidermal surface merocrine secretion hypotonic and slightly acidic Active from soon after birth
Types of skin sensory receptors
mechanoreceptors, thermoreceptors and nociceptors
epidermis
keratinised squamous epithelium
dermis
connective tissue layer
has nerves, blood supply and fibroblasts, sweat glands and hair
how are damaged cells replaced in the epidermis
continually shed, and constant proliferation of cells in stratum basale which move up to the top, to replace lost cells
Meissners corpsucles
v sensitive mechanoreceptors
found on palms
what type of secretion for sebaceous glands
holocrine
